Why do I get a hard edge when mixing a Transparent and Glossy node with a Fresnel node?
You can change the alpha blend mode, currently you are in Alpha Clip which rounds the alpha value to 0 for values &lt; 0.5 and to 1 for values > 0.5.

Make sure your render engine is set to Eevee first :



Alpha Clip :



Alpha Blend :



If you want to tweak it further, add a Color ramp between the Fresnel and the mix shader, set to B spline interpolation, and move the white cursor way to the left :



Note you can get the same setup with a principled BSDF, which will be more physically correct :